Dar es Salaam — There is a decline in the prevalence of parasites causing malaria in Africa, a new study published on Wednesday October 11 in the Journal Nature shows.

It's said to be the largest-ever data-set spanning 115 years. Findings include results of 7.8 million blood samples collected across 37,000 locations in 43 countries, including Tanzania.

Lead author of the study, Prof Robert Snow of the Kenya Medical Research Institute (KEMRI) in Nairobi and his colleagues gathered data from the past 115 years on the prevalence of a malaria parasite, Plasmodium falciparum.

The researchers, however,say malaria in Africa is still complex and predicting the future of the disease based on climate or economic development alone would be foolhardy.

They note that the malaria infection rate has generally declined in sub-Saharan Africa, from 40 percent of those examined in 1900-29 to 24 percent in 2010-15.

Read: Declining trend of malaria in Tanzania: Should we celebrate or worry?

The researchers analysed the data to estimate the malaria infection prevalence for each of 520 administrative units of sub-Saharan African countries and Madagascar for 16 periods since 1900 through to 2010-2015.

In a press statement released alongside the study, Prof Snow said:"People often focus on recent history in tracking malaria in Africa to inform donors and control programmes on recent actions. The longer history of malaria in Africa allows us to put into context the recent decline."

"The history of malaria risk in Africa is complex, there have been perfect lulls, when drugs worked and drought prevented mosquitos' transmission infection; there have been perfect storms, when drugs stopped working and flooding affected large parts of Africa."

"It has been a history of long-term cycles and predicting the future of malaria in Africa based on climate or intervention coverage alone is difficult," Prof Snow further explains.

For his part, the co-author of the study, Dr Abdisalan Noor said: "Shown in context, the cycles and trend over the past 115 years are inconsistent with explanations in terms of climate or deliberate intervention alone. The role of socio-economic development, for example, remains poorly understood."

According to the history, there were two periods of rapid decline in infection, coinciding with the introduction of two major anti-malarial compounds between 1945 and 1949 and the widespread introduction between 2005 and 2009 of bed nets treated with insecticides and a new combination drug treatment.

Resurgence of the disease between 1985 and 2004 can be attributed to the spread of drug resistance, unusual weather events and lack of investment in prevention.

The team notes that large areas of West and Central Africa still experience high rates of malaria transmission and warn against crediting the most recent decline in malaria prevalence to human intervention alone.

The study reveals that the biggest historical drop in malaria parasites followed the Second World War with the discovery of DDT and chloroquine; and then in 2005 with the rolling out of insecticide treated bed nets and new drugs to treat malaria.

The malaria prevalence was low during the late 1960sthrough the 1970s and the early 1980s. This was a period, when despite the international community abandoning investment in malaria control in Africa, chloroquine use was widespread with repeated dosing available to the general population.

Chloroquine resistance expanded across Africa in the 1980s and in the late 1990s unprecedented rainfall led to flooding and major malaria epidemics. Ministries of Health across the continent woke up to the perfect storm without any significant mosquito vector control in place. The malaria prevalence returned to the levels seen before the Second World War.

It took further five years for the international community to provide free insecticide treated bed nets and effective malaria treatment.

The financial response by the Global Fund and technical revisions to policy by the World Health Organisation after 2005 led to one of the largest drops in malaria infection prevalence witnessed since 1900.

The findings caution about projecting of the future of malaria in Africa. The current prevalence of infection, 24 percent, is at its lowest in 115 years, but gains have stalled since 2010 and 240 million infected individuals remain a substantial burden.

However, they say little has changed in the high transmission belt across West and Central Africa. Emerging insecticide and drug resistance and growing international ambivalence to funding control further increases the risk.

The researchers urge new tools for the poor and high malaria burden areas of Africa, a focus on eliminating malaria in the low burden margins of Southern Africa or small islands across the world or run the risk that high burden countries in Africa being ignored and left behind.

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